Packet or cell switched data network elements such as routers transmit between each other data transmission packets or cells that contain management or control messages. The operation of a data network is monitored by means of control messages, and possible errors in operation can be detected. The network elements that monitor the network by means of management messages can control the parameter settings of the network elements under control and gather the statistic data collected by the said network elements. In addition, the network routing topology can be adjusted by the management messages.
In this document, data transmission packets and cells containing management or control messages are called protocol packets. Protocol packets are used for instance in the BFD protocol (Bi-directional Forwarding Detection Protocol), by which network can for example control that a data transmission link between adjacent network elements, a route between two points in the data network or a tunnel defined in the data network is in proper order for operation.
A modern network element such as router generally includes several functional units, such as line cards, switch cards and control cards. A single functional unit includes one or more protocol processor that can be realized by an ASIC circuit (Application Specific Integrated Circuit), an FPGA component (Field Programmable Gate Array), a programmable network processor NPU (Network Processing Unit), a general purpose programmable processor or a combination of one or more of the following. The task of a protocol processor is to perform the processing operations of the data transmission packets received in the network element and of the data transmission packets transmitted from the network element, such as the selection of the correct transmission port on the basis of the target address provided in the data transmission packet.
In a situation where the network element has only one protocol processor, it is naturally possible to be sure that each protocol packet arriving in said network element must be processed by said protocol processor. The situation becomes more complicated, if the network element has several protocol processors, of which each processor operates the management or control sessions assigned for said protocol processor. Now there can arise a situation where a protocol processor A provided in the network element receives a protocol packet that represents the management or control session operated by a protocol processor B also provided in said network element. Said management or control session controls for example a data transmission channel, route or tunnel terminated in said network element.